Machine vision technology is widely used to replace the human eye in extracting information from an image. In machine vision systems, an image is captured, and then image-processing techniques are used to extract the required information from the image. Certain inputs, such as measurement and control inputs, may also be used during the processing of the image. The illumination device for the subject being captured is an important factor that determines the quality of the image captured, and, therefore, the quality of the extracted information. Collecting a good, high-contrast image cannot only greatly reduce the workload of the image processing, but also can greatly improve the accuracy and speed of the extraction of information during the image processing. Currently, annular light sources are used in machine vision lighting systems. These annular lighting systems are basically fixed diameter, so the diameter of the light source is unchangeable when the environment changes or characteristics of the subject under illumination change. The diameter of the light source is an important factor in providing even illumination, so if the environment changes, for example, the distance from the light source to the subject changes, a fixed-diameter light source tends to provide uneven illumination, resulting in poor image acquisition.